Create scheduled github action to merge up stream branch

Author: anthonychwong

.github/workflows/scheduled-merge.yml

@@ -0,0 +1,31 @@
+name: Merge upstream branches every Thursday 00:00
+on:
+  schedule:
+    - cron:  '0 */12 * * *'
+jobs:
+  merge:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          persist-credentials: false
+          token: ${{secrets.GHPAGE_SECRET}}
+      - name: Merge upstream
+        run: |
+          git config --global user.name 'GitHub Action by Anthony'
+          git config --global user.email '[email protected]'
+
+          # "git checkout master" is unnecessary, already here by default
+          git pull --unshallow  # this option is very important, you would get
+                                # complains about unrelated histories without it.
+                                # (but actions/checkout@v2 can also be instructed
+                                # to fetch all git depth right from the start)
+
+          git remote set-url origin https://${{secrets.GHPAGE_SECRET}}@github.com/anthonychwong/gbgwcalculator
+
+          git remote add upstream https://github.com/rmkane/gbgwcalculator.github.io.git
+          git fetch upstream
+
+          git checkout master
+          git merge --no-edit upstream/master
+          git push origin master